1. Field of the Invention
This invention relates generally to method of forming photoresist anti-etching ability, and particularly relates to method for increasing process window and reducing required thickness of photoresist.
2. Description of the Prior Art
For etch process, as FIG. 1A shows, photoresist 12 and etched layer 11 are formed on substrate 10 sequentially, pattern of photoresist 12 defines which part of etched layer 11 would be removed by etch process. Obviously, to ensure etched layer 11 and photoresist 12 have same pattern after etch process is finished, pattern of photoresist 11 should not be changed while etch process being performed.
However, photoresist 12 also is removed by practical etch process, especially edge of opening 13, although removed rate of photoresist 12 usually is obviously smaller than removed rate of etched layer 12. Thus, after etch process is finished, flowing cases may be happened. As FIG. 1B shows, although thickness of photoresist 12 is decreased, pattern of photoresist 12 is correctly transferred into etched layer 11. As FIG. 1C shows, although thickness of photoresist 12 is decreased and pattern of photoresist 12 slightly changed, pattern of photoresist 12 is essentially correctly transferred into etched layer 12. As FIG. 1D shows, both thickness of photoresist 12 is decreased and pattern of photoresist is changed, to let pattern of etched layer 11 is significantly different from pattern of photoresist 12. Indisputably, the more thickness of photoresist 12 is, the more removing rate of photoresist 12 is, the less distance between neighboring opening 13 is, and then the more cases of FIG. 1C or FIG. 1D are, to let assurance of etch process is decreased.
Because pattern of photoresist 12 is dependent on configuration of semiconductor and is not adjustable, also because distance between neighboring openings 13 is decreased while critical dimension is decreased, the most direct solution of previous problem is increasing thickness of photoresist 12. However, whenever thickness of photoresist 12 is increased, difficulty and cost of photolithography also are increased, and then production is decreased. Therefore, increasing thickness is not a general solution for all photoresist 12, especially while both thickness of photoresist 12 and width of opening 13 let aspect ration of opening 13 is too large to be properly formed.
Another often-seen solution is to harden photoresist 12 by ultra-violet light (UV), especially to harden surface of photoresist 12 to let anti-etching ability of photoresist 12 is increased and removed rate of photoresist 12 is decreased. As FIG. 1E and FIG. 1F show, after photoresist 12 is formed and before process is not started, photoresist 12 is exposed by ultra-violet light 14 to let surface of photoresist 12 is transferred to hardened photoresist 15. After that, etch process is performed by using both photoresist 12 and hardened photoresist 15 as required mask. Because removed rate of hardened photoresist 15 is smaller than removed rate of photoresist 12, after etch process is finished, thickness of both residual hardened photoresist 15 and residual photoresist 12 is smaller than thickness of residual photoresist 12 which is not hardened. Thus, disadvantages such as thinner photoresist 12 and changed pattern could be effectively improved.
However, while photoresist 12 is hardened by ultra-violet light, following disadvantages still are unavoidable. First, ultra-violet light 14 only could harden surface of photoresist 12 and then thickness of hardened photoresist 15 is finite, thus, photoresist 12 still must be thick enough to ensure pattern could be accurately transferred after hardened photoresist 12 is totally consumed. Second, glow discharge of etching process is in the range of near ultra-violet light, which would reduce thermal stability of both photoresist 12 and hardened photoresist 15 and induce unavoidable deformation. Third, absorb efficiency of ultraviolet light depends on material of photoresist 12 and then different material requires different wavelength of ultra-violet light, thus, not only fabrication is complicated for wavelength of ultra-violet light must be adjusted but also some materials of photoresist could not be properly hardened by ultra-violet light. Fourth, temperature of expose process under ultra-violet light is high, shape of photoresist 12 maybe changed. Fifth, power of ultra-violet light is low for most available ultra-violet sources of practical fabrication line, then required period for exposing under ultra-violet light is long and efficiency of fabrication line is decreased.
In short, each of current technologies for solving consumption of photoresist during etch process is not perfect, and then it is desired to develop new technology for enhancing anti-etching ability of photoresist.
One main object of this invention is to present method of forming photoresist anti-etching ability.
Another main object of this invention is to present a method for increasing process window and reducing required thickness of photoresist.
Still one main object of this invention is to present a method of etching with anti-etching photoresist.
This present invnetion provides a method of enhancing photoresist anti-etching ability, especially is a method which is performed before etch process, at least includes follows. Provide a substrate and form a photoresist with a pattern on the substrate, then put both photoresist and substrate in a low pressure environment, and then treat photoresist by an electron beam to let at least part of photoresist is hardened. After photoresist is treated by electron beam, photoresist is hardened and has anti-etch ability, thus, precision of etch process is enhanced and corresponding pattern is more precise.
Other preferred embodiments are methods of etching with anti-etching photoresist. One embodiment at least includes follows. Provide a substrate, wherein a patterned photoresist is located on, and simultaneously perform an electron beam expose process and an etch process, wherein electron beam exposes process exposes patterned photoresist by electron beam and etch process uses patterned photoresist as a mask. Another embodiment at least includes follows. Provide a substrate, wherein a patterned photoresist is located on, and alternately perform numerous electron beam expose process and numerous etch process, wherein electron beam exposes process exposes patterned photoresist by electron beam and etch process uses patterned photoresist as a mask. Obviously, in both previous embodiments. Hardened photoresist is continuously consumed but also is continuously formed.